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Data may exist in much form. You may have data in relational tables residing on a relational database or portable data in form of XML. Since data exist in many forms, obviously there are many ways to manipulate or access them. One of the most popular ways of sharing data is as XML.

Considering prominent presence of XML as way of data sharing, LINQ to XML got introduced in C# 3.0 to work effectively and efficiently with XML data. LINQ to XML API contains classes to work with XML. All classes of LINQ to XML are in namespace System.XML.Linq.

Objective of this article is to understand, how could we work with LINQ to XML?

Let us start with below image. It depicts an isomorphic relationship between XML elements and cross-ponding LINQ to XML classes.

XML Element is fundamental XML constructs. An Element has a name and optional attributes. An XML Elements can have nested Elements called Nodes also.

XML Element is represented by XElement class in LINQ to XML. It is defined in namespace System.Xml.Linq. And it inherits the class XContainer that derives from XNode. Below tasks can be performed using XElement class

It can add child element.

It can delete child element.

It can change child element.

It can add attributes to an element.

It can be used to create XML tree

It is used to serialize the content in a text form

XElement class got many overloaded constructors. You can pass XAttribute to create XML elements with attribute.

If you examine below code snippet, I am creating XML with root element Root and many child elements. Child Element Data1 and Data2 got attributes name and ID respectively with value Dj and U18949

Code Listing 1

XElement xmltree = new XElement("Root",
new XElement("Data1", new XAttribute("name", "Dj"), 1),
new XElement("Data2", new XAttribute("ID", "U18949"),
new XAttribute("DEPT","MIT"),2),
new XElement("Data3", "3"),
new XElement("Data4", "4")
);
Console.WriteLine(xmltree);

On executing above code you should get below output,

Let us stop here and examine how Attributes of XML is mapped in XAttribute of LINQ to XML. XML Attribute is a Name/Value pair associated with XML elements. XAttribute class represents XML Attributes in LINQ to XML. XAttribute class is overloaded with two constructors. Most frequent used constructor is one takes name and values as input parameter. In CodeListing1 , attributes to element is being created using XAttribute class.

A XML tree can be constructed using XAttribute and XElement class.

Assume you have a list of Authors as below code listing, Author is a custom class.

Above code snippet will create Authors as root element. There may be any number of Authors as child element inside root element Authors. There are two other elements Name and NumberOfArticles are in XML tree.

There may be scenario when you want to create XML tree from a SQL Server table. You need to follow below steps,

By this point you know various ways of constructing XML tree and saving on file system. Now next thing come to your mind would be how to parse XML files using LINQ.

Parsing of XML document means reading XML document, identifies the function of each of the document and then makes this information available in memory for rest of the program. XElement.Parse () methodis used to parse XML. This is an overloaded method. This takes a string input parameter to parse. Second overloaded method takes extra input parameter LoadOptions. LoadOption defines where to preserve space in information or not?

After knowing all the pieces of LINQ to XML, let us go ahead and find how we could put all information we have so far to bind information from XML file to DataGrid of Silverlight. It is a common requirement when you need to bind or display data from XML File to Silverlight Data Grid.

Essentially there are three steps you need to execute to bind XML to Silverlight Data Grid.

Download content of XML file as string using WebClient class.

Parse XML file using LINQ to XML

Bind parsed result as item source of Data Grid.

Very first you need to prepare XML file as data source. Put XML file in bin folder of Silverlight project. However you can parse XML file from remote location as well.

We are going to bind Data.xml residing in client bin folder to Data Grid.

XML can be parsed as below. On examining below code, you will find XML file is loaded using XDocument. After loading file is being traversed using Descendants method. On getting the values for each Student node, you need to create instance of Student and add it to the list of Student.

Sometime you may have requirement to put certain style rules to tags when they are nested in other tags. For example; you want to make UL as square if it is nested inside an OL. You can very much do that in HTML 5 as below,

You can apply rules to tags nested to any level. For example if you want to apply h1 tag inside a ul tag and ul tag is inside ol then you can apply very much like below,

In below HTML , rules [color red] being applied to tag h1 nested inside ol and ul . whereas there is no rule for usual h1.

When you view in browser above HTML you will get expected rendering as below. Please notice that “Hello HTML 5” text is rending with usual h1 whereas TWO A is in the color red.

Creating Classes and Id for Style

So far we are creating rules for a particular tag and setting it as style. There may be scenario where you do not want to apply style to all appearance of tags in a particular document. For example you are listing all the students and want to set color red only for students enrolled newly. In that case you have two choices

Apply style to each new student item manually

Create a class and apply to the new students. What advantage you get here is that if tomorrow you want to change color from red to blue, you will have to change only at one place.

You can either create class or Id. Both mark a certain element to refer then in style sheet.

In pervious approach I traversed manually in Syntax Tree to the Method level and started from Compilation Unit level to get the Method Arguments. Rather than manually navigating the Syntax Tree, you can use LINQ to get the parameter in the function. We can directly apply LINQ on Syntax Tree.

If you remember from last post out Syntax Tree was as below,

Now if we want to print method name using LINQ in Syntax tree then,

Underneath LINQ is also doing the manual traversing of the Syntax tree. When you execute above code you will get output as below,

If you have more than one parameters in the method then you can print them like below,

And then you can traverse using foreach to print all the method names. For your reference all the code discussed in this post is given below,

Conditional reading of BLOB implies, you want to read BLOB only when BLOB is modified. There are scenarios when you need to read BLOB frequently. In that case to avoid network usage and bandwidth, you may consider reading BLOB only when BLOB has been modified since last read or download. This type of BLOB reading is termed as Conditional BLOB reading.

Usually to read or download BLOB, you create reference of BLOB as below

In above code snippet

ConnectionString is connection string to your storage account.

Containername is name of the public container.

Doc1.docx is name of the BLOB.

If you want to read it without any condition or in other words you want to read the BLOB regardless of whether it has been modified or not then you can read it in byte array as below,

As of now everything is fine for unconditional read but if you want to do Conditional read on the BLOB then you will have to use ,

IfNoneMatch

eTag

IfNoneMatch is a static variable of AccessCondition structure. When you download a BLOB you can additionally provide BLOBRequestOptions. Almost all Download functions are overloaded with BlobRequestOptions.

If you don’t specify BLOBRequestOptions then you will perform unconditional read.

To perform conditional read, you need to follow below steps,

Step 1

Save ETag value from the server at time of first reading in a local variable

Step 2

Create instance of BLOBRequestOptions with setting AccessCondition as below,

In above code we are passing locally saved ETag value to IfNoneMatch

Step 3

At time of making second call onward to download BLOB pass Request Option as below,

If BLOB is not modified then you will get into the Exception

At time of downloading BLOB in above code, server will fist check for the ETatg in IfNoneMatch header. If server don’t find new version, it will send HTTP 304 request to the storage library.

For your reference full source code of conditional BLOB reading is as below,

Recently Microsoft released Roslyn CTP and you can download it from here. You can learn more here

In this post, I will focus on Roslyn Syntax API.

Syntax Tree is used by the compiler to understand the language constructs.

Syntax Tree exposed by Roslyn Syntax API is immutable. So to use it as a developer you can consume it on multiple threads without much thinking about concurrency measures and all.

Essentially; Roslyn Syntax API exposes below classes.

Let us now explore each of classes and structure exposed by Roslyn Syntax API one by one. Create a Roslyn Console Application. Once you install Roslyn CTP, you will get Roslyn project template installed. Choose Console Application from installed template.

Let us create a compilation unit called Animal. We will pass this class to create syntax tree and do the evaluation.

You can pass class Animal as string to SyntaxTree class

Have you noticed two times double quotes before Animal in print statement

If you execute below statement you will find returned syntax tree is the compilation unit.

Variable tree is the instance of SyntaxTree class.

Expected Output

Typecast returned root to CompilationUnitSyntax and put a breakpoint to analyze more what Roslyn syntax API returns .

You will notice there are 0 counts in using directive since we are not having any using directive in the input text (Animal class) to the SyntaxTree ParseCompilation. In count of Member you will find 1.

To get the First member you need to fetch it as you are fetching usual array with the index value.

In our case we have only one member and that is Animal class. So first print statement will print the class and second statement will print the type that is Class Declaration.

Expected Output

Since kind of member is ClassDeclaration so typecast it to ClassDeclaration to evaluate it more.

And if you put breakpoint and execute it you will find there are Members, Keywords, and Identifier etc. for ClassDeclarationSynatx also. Count value for Members is 1. This value is 1 because there is one function in Animal class.

When you print kind of FirstMethod as below,

Expected Output

Put breakpoint on FirstMethod variable, you will find number of parameters count to 1. In Animal class , Display method has one input parameter.

To print input parameter you need to traverse the syntax tree as below

Expected output

In this way you can harness all the capability and features of Roslyn Syntax API to do reverse engineering on your code. For your reference all the source code discussed in this article is given below.